One of the most commonly used C library function is the printf() function which allows to write text to the “standard output” (normally a monitor or line printer). In embedded systems, often a UART is used. In Arm Cortex-M based systems you can redirect the standard output to the ITM debug channel which saves resources (the UART) and is much faster. In µVision, you can use the “Debug printf() Viewer” window to observe printf() messages delivered via ITM.